1. Field of the Invention
The present invention relates to a wood chip board containing an aminoplast resin as binder, and also to a process for the preparation thereof.
2. Description of the Prior Art
The properties of wood chip boards are determined to a substantial degree by the binder combining the wood chips. Among these properties are, e.g., the strength values, the resistance of the boards to moisture and also the amount of chemically free remnant formaldehyde, which is even present in the binder after completion of the compression step. This amount of formaldehyde may cause highly undesirable environmental contamination if it escapes from the board. The properties of the boards are especially affected by the amount of the binder used, by the distribution thereof on the chip materials and by the degree of curing which occurs when the chip material is compressed. The composition of the binder also has a considerable influence on the properties of the boards.
Usually an increase in the amount of binder increases the strength values and also the resistance of the board to moisture; however, the binder is expensive compared to the cost of the chip material and this results in an increased expense, and, depending on the number of boards, also involves a higher amount of unreacted formaldehyde. In attempts to counteract the disadvantageous effects of free formaldehyde in the binder, hitherto the amount of the co-reactant for the formaldehyde present in the binder (e.g., urea or melamine) has been increased at the expense of the formaldehyde, so as to achieve as complete a bonding of the formaldehyde as possible in the course of the hot pressing step in which the boards are formed and cured. However, in this case, the increased expenditure for the increased amount of co-reactant in the binder is borne without enhancing the strength or resistance of the board.
Attempts have also been made to improve the properties of wood chip boards. For example, increased strength with a simultaneous decrease in the amount of free formaldehyde in the binder has been obtained by providing a longer compression period in the course of preparing the boards. This however, leads to a substantial increase in production expense, as the presses are an extremely high capital investment. Thus, it is necessary to try to get by with a compression period which is as short as possible.